Process and device for producing moldings, in particular for structural elements, insulations and/or packaging, and moldings so obtained

ABSTRACT

The invention relates to a process for the manufacture of new shaped parts, preferably made from chipboards, wherein a mass formed from at least a binder and a small-particled material brought into contact with this binder is subjected to extrusion at elevated temperature and pressure. In the process according to the invention, a mass possessing a total moisture content of 6 to 25 wt. % or adjusted to the stated moisture content and made up of at least one biopolymeric preferably starch-containing binder, which converts into a melt and/or gel at extrusion temperatures and pressures, and further made up of the small-particled material, is subjected to extrusion and immediately thereafter undergoes decompression and spontaneous expansion. A device for carrying out the process according to the invention is also disclosed, and includes extrusion equipment for lump-sized starting components having a processing zone arranged upstream of an extrusion nozzle for carrying out partial decompression, thereby causing partial internal expansion of the mass being processed.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The subject of the invention is a process for the production of newshaped parts used for the production of construction material,structural material or packaging material, preferably made from woodchip and/or fibre-based sections and/or boards, also the equipment forproducing the parts and the use of the said parts.

2. Description of the Related Art

Many procedures are known by means of which biopolymeric products may bebroken down in order to process them in a separate, second work stepinto other products, e.g. wood-fibre boards. The biopolymeric productsare broken down by the application of steam followed by decompression ormechanical comminution. Usually a combination of these two methods isused. The serious drawbacks of both these processing methods are thatthey require high inputs of energy and also that the intermediateproducts obtained can only be processed in batches.

Other processes are known in which a mass consisting of resin and woodchips is extruded to produce structural boards. Specially designedextruders, and especially extruder screws, have to be used for thispurpose. In most cases, only semi-finished products are produced and noattempt is ever made to produce the final product in one singleoperation. The expense involved in having to provide separate machineryfor the final products adds to the expense of the boards, wall elements,etc. which are extruded on the known machinery.

Reference is made here to German Patent Application DE-A1 1 653 263which can stand as an example of the known extrusion processes forproducing boards and sections from material containing lignocellulose.According to that Patent Application, wet raw material in the form ofchips is first dried in the drying mixer to the desired moisture contentthen mixed with glue in at least one mixer, and only after abinder--specific materials are mentioned in the Patent Application--isapplied in a separate wetting step is the raw material continuouslyextruded in a screw extruder while continuously adjusting the pressureand while also regulating the temperature, to form the finished product.

For the manufacture of a cigarette-like product, the concept is known ofcompressing a moist mixture of natural fibre-shaped material and starchin an extruder until the starch melts to form a gel which is thenallowed to expand to give a foam-like product made of biodegradablesubstances, cf. EP-A 113 595.

Furthermore, it is known from US-A 4 357 194, that a mixture of naturalfibre-shaped or fibre-containing material and starch or sugar may becompacted and heated with steam in order to obtain particle boards madefrom biodegradable substances, without using artificial glue(adhesives). In addition, US-A 4 627 951 describes processes by means ofwhich natural, sugar-containing, fibre-shaped material may be compressedin heatable board-pressing machines, without steam and without theaddition of glue, to obtain particle boards made of biodegradablesubstances.

The disadvantage of the chipboards produced by the known procedures isthat they have a high density which makes them heavy and awkward tohandle when they are used, for example, in the construction of smallitems of furniture; furthermore, they are not very well suited for usein thermal insulation applications e.g. as floor, wall and ceilingboards, attic lining materials etc.

Another large area is accounted for by the production of insulationboards--preferably of low density--from foamed plastics, which varywidely in their properties, whose porosity is obtained by gas-generatingprimary components or additives The disadvantages of such products arethat their mechanical strength declines rapidly at low density, theymelt and burn easily their resistance to chemicals is inadequate and,last but not least, they do not break down readily once they aredisposed of as waste. What is more, the above-described fibre boards canalso cause environmental problems right at the manufacturing stage, dueto the chemicals used, as well as later when they are employed in theirintended applications.

SUMMARY OF THE INVENTION

The purpose of the invention is to avoid the disadvantages of thealready known processes and products in this sector, while using thecustomary extrusion machinery, but without the separate priorapplication of glue to the chip or fibre material, and to create aprocess which permits the products mentioned at the beginning of thisapplication to be produced in essentially one single operation fromenvironmentally friendly raw materials. The aim is to obtain productswhich exhibit a greater degree of isotropy and thus have more uniformphysical properties than the previously known boards, and which alsocombine lower density with greater mechanical stability.

In the process according to the invention, the new products are obtainedin a particularly advantageous manner.

In this connection, it is particularly important to form a genuinemolten gel by applying heat and pressure so that the preferablystarch-containing materials or other binder materials capable of forminga melt--such materials may also include starch itself--may be feddirectly into the extruder, after the desired moisture content has beenadjusted, in solid, lump form, such as whole rice grains, possiblytogether with the husks which serve as the fibre material component, orsimply uniformly mixed with the other biogenic chip or fibre material,e.g. wood chips, straw, cardboard, paper and similar. The products canthus be produced in practically one operation. Apart from the chipped,comminuted, defibrated, fibre-like, fibre-containing and fibre-shapedmaterials referred to above, the biogenic high-molecular materials alsoinclude materials such as rubber and similar which also possessfibre-like molecules.

By converting the binder, which is added in solid form, into a moltengel consistency, it is possible, despite the expansion which immediatelytakes place, to process the material without any difficulty on a widerange of different types of extruder. The product is smoothed by bindingthe biogenic materials used, e.g. wood chips, into this highly viscousphase. The process is easy to control and yields products having apleasing surface finish, low density and high strength. The formation ofthis gel-like consistency can also be promoted by additives, e.g. agentswhich cause cellulose to swell or dissolve, which do not themselvespossess the ability to gel, but which bring it about in one of the othercomponents, e.g. in the wood chips, when the material is intensivelyworked in the extruder.

The new products obtained by the process according to the inventionoffer the special advantage that their specific mass can be controlledby varying the degree of expansion, which can be influenced over a widerange via the pressure and heat applied, and in this way a much lighterwood-fibre board can be produced which is only slightly less strong thanother fibre boards.

Immediately after the product emerges from the extruder, which can befitted with any desired shape of extrusion nozzle, in particular a flatnozzle, the gel, especially a starch gel, starts to make the transitioninto a glassy state as it cools, while simultaneously the steamgenerated by the water vapour trapped in the extrusion mass undergoesexpansion. By adjusting the moisture content, starch component,biopolymer content and the operating conditions, these two competingprocesses can be precisely matched to one another in order to obtainoutstanding final products. One last major advantage is that the finalproduct can be made to expand to the desired density without the needfor additional gas-generating or gas-releasing chemicals, but simply viathe moisture content of the extrusion mass, e.g. of the wood chipsand/or the starch.

The invention can also be particularly advantageously used for themanufacture of packaging filler materials and throw-away thermalinsulating containers, e.g. for snack foods, etc. The products obtainedby this process are characterized by their pleasing appearance to theconsumer; they also possess good shock-absorbing and elastic properties,which are particularly important when the products are used as fillers,e.g. chips or spheres, in packages, or also when they are used aswrapping elements or foils. Another advantage is their "crisp"consistency, which makes it much easier to comminute them, e.g. forwaste disposal purposes, and thus also enhances their biodegradability.

When the method according to the preferred embodiment is used, thestarch is employed as the binder and can be at least partially replacedby starch containing plant parts taken from the group consisting ofcereals, grains, and starch containing roots, tubers and stems, eithercomminuted or in their natural state. The fibrous material is selectedfrom the group consisting of wood chips, plant fibres, cellulosematerials, recycled cellulose materials, paper materials and recycledpaper materials. When plant fibre materials are used, on the one handhigh-grade chip or fibre products are obtained, and on the other hand agreat deal of flexibility is possible in the choice of startingcomponents and in the quality of the expanded finished products, wherebyin particular economic advantages are also achieved.

If the process temperatures are adjusted, in the extruder totemperatures in excess of 100° C., and in particular in the range of125-250° C., the amount of internal energy needed to permit a controlledexpansion, coupled with the competing solidification of the mass to thedesired density, can be applied in a favourable manner to the moisturecontent. When the pressures are maintained as outlined in this Claim,controlled expansion can be very easily and advantageously attained.

In another preferred processing method the mixture is subjected to aspecific mechanical energy input of 0.05-0.7 kWh/kg, and in particular0.1-0.3 kWh/kg, and no separate device is needed to heat the mass in theextruder; in addition, because the edges, corners and projections on thelumpy, fibre-containing material are rounded-off, the mass takes on a"smooth" consistency, to which reference has already briefly been made,at the nozzle, and this minimizes the problems of extruding masses ofmelt-like consistency containing coarse filler materials.

"Lightweight" but structurally rigid boards and sections can beadvantageously obtained by performing decompression in order to obtainthe preferred values in the expansion index of at least 1.1 andpreferably 2-8.

When 5-85 wt. %, and preferably 10-50 wt. % biopolymeric binderbiopolymeric binder is used in the mixture, a wide range of chip andfibre-containing materials can be used while still attaining thenecessary workability of the extrusion mass along with adequatemechanical properties of the lightweight structural elements which areproduced.

In order to ensure that the expansion process can be advantageouslycontrolled in a wide variety of ways, a liquid expansion agent which ismiscible with water, such as certain alcohols or ketones, may also beadded to support the expansion effect of the moisture content in theextrusion mass itself. These alcohols and ketones boil in the range of70 to 180° C. under atmospheric pressure.

If shaped parts such as boards and sections are produced, in a preferredmanner, with water-repellent and thus also anti-microbial modifiers, theproducts will have a long lifetime but they can still be disposed of ata later date as waste without any problem. For example, by incorporatingrubber or silicone molecules, it is possible to produce shaped parts oflow density and having a soft but dimensionally stable and even anelastic consistency.

The same holds true for a mixture containing at least one bi- orpolyfunctional modifying agent capable of forming cross-linking bridgesbetween the molecules of the binder, under the conditions of extrusion,wherein the modifying agent is selected from the group consisting ofshort-chained di- or polycarboxylic acids, di- or poly(thi)ols and theirderivatives, molecules containing tertiary amino acid groups, andpolyphosphoric acids. By using this mixture, the lifetime of theproducts can be extended, but also in a preferred manner the appearanceof the new shaped parts can be modified, by directly incorporating themodifying agents into the molecular structure of the binder.

When the surface of the extruded product made from the molten gelmixture is coated with a peripherally supplied coating mass before theproduct emerges from the extruder, shaped parts are obtained whichdiffer from the basic parts in that they have, for example, a tough,elastic or other kind of "rind", "skin" or surface layer. The process ofapplying an adhesive, such as hot cross-linking resins, or similar,which is also referred to in this Claim, may be advantageous if anycoating is to be applied after extrusion, as is done in the case ofchipboards and structural boards.

Boards, sections, etc. provided with surface finishes--e.g. fordecorative purposes--can be advantageously produced in accordance withthe present invention, the advantage being that the extrusion devicedoes not have to be modified to permit the addition of a coating massbefore the extrusion mass has left the extruder.

By limiting expansion of the part immediately after formation,dimensionally accurate shaped parts may be obtained in an advantageousway, even if unavoidable fluctuations occur in the raw materials used,e.g. their particle size or grain size or the moisture content, etc.

If a surface coating is applied or bonded to boards and sectionsproduced in accordance with the present invention the desireddimensional accuracy of the extrusions is reliably combined in atechnically simple and cost-saving manner with the advantages of asurface finish which is exactly matched to the later uses to which theproducts will be put.

A further important and preferred subject of the invention is a machinefor manufacturing the aforementioned shaped parts, with devices forcomminuting and/or conditioning and/or pre-mixing the startingcomponents, which are preferably supplied in solid form as lumps orsmall pieces, along with other devices for feeding these components intoan extrusion machine, especially a multi-screw extruder possibly havingscrews with alternating leads and/or a conical configuration, and havingalso at least one shape-imparting, preferably rectangular extrusionopening.

This machine is fitted with a means for comminuting, conditioning, andpre-mixing the starting components and also with a means for feedingthese components to an extruder having at least one shape-determiningextrusion opening. The screw extruder includes means for supplyingsolid, lump-shaped or small-particled starting components, and beingprovided upstream of the nozzle with a processing zone in which partialdecompression of the mixture is carried out. An extrusion machine ofthis type offers the advantage that the dimensions of the expanded partscan be controlled with great accuracy and the whole process runs more"smoothly". The partial decompression is achieved by providingappropriate areas in the screw where the lead of the screw is increased,or by providing larger "free" transportation volumes between therotating screw and the wall of the extruder.

The machine preferably includes a dimension limiting means downstream ofthe extrusion opening for limiting the spontaneous expansion of theextruded part, wherein the dimension limiting means includes a roller orcontinuous belt element that can be brought or adjusted to therespective speed of advance of the extruded part. This constructionoffers the advantage that it is simple in design and construction but iscapable of guaranteeing the dimensional stability of the product whichis dimensionally not very easy to control during the production process.

In accordance with another aspect of the invention, the dimensionlimiting means is oriented transverse to the direction of movement ofthe extruded part and is provided with a non-stick surface that permitsthe means to rotate at a speed matching the speed of the extruded part.Thus, while the device is simple in design and construction, it is notnecessary to provide a separate drive mechanism for movingdimension-limiting elements at a speed conforming to that of theextruded products.

If the surface smoothness or similar of the product has to meet stricterrequirements, then a more complex embodiment of the production systemmay be used, wherein the dimension limiting means is a wall element orendless belt having a non-stick, smooth or structured surface running atessentially the same speed and in the same direction as the extrudedpart.

A significant reduction in the technical effort which would otherwise beneeded for applying a foil coating to the shaped part may be achievedwith a variant of the design, wherein a device is provided forcontinuously feeding product-coating foils into the gap between thesurface of the product and the roller of the dimension limiting deviceat a speed essentially equal to the rate of advance of the extrudedpart. This construction permits a high degree of dimensional precisionto be combined with the surface-finishing technique.

The application of a surface finish other than a foil coating, e.g. acoating mass or a similar kind of powder, precisely at the moment afterthe product has left the extruder nozzle and the expansion commences andcontinues, is problematical but the problems involved can be avoidedwhen the machine has several feed pipes discharging close to the nozzleinto the exit area of the extruder chamber, wherein the pipes aredistributed around the inner periphery of the chamber and supply surfacecoating and/or gluing media under pressure.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention, and in particular the preferred types of devices neededto accomplish it, will now be described on the basis of the drawings,wherein

FIG. 1 shows an oblique-angled view of the most important parts of aninstallation according to the invention for the production of expandedfibre boards, wherein the installation is equipped with a deviceconsisting of rollers for limiting the cross-sectional profile of theproducts; and

FIG. 2 depicts a section of an installation, also according to theinvention, in which the profile-limiting elements consist of wallelements in the form of continuous belts.

DESCRIPTION OF THE PREFERRED EMBODIMENT(S)

According to FIG. 1, wood chips, starch-containing binder and"additives"--all in solid lump form or as small particles--are fed inthat order from storage hoppers 101, 111 and 121 via feed belts 10 and11 and also feed screw 12 into the storage hopper 21 of the extrusionmachine 2. From here, the mass is continuously fed into the work chamberof a two-screw extrusion press 2 equipped with drive 22, and premixingof the starting components takes place in the entry zone 201 of theextruder, right after storage hopper 21. In the immediately followingsealing zone 202, on the one hand the moisture content is temporarilyprevented from converting back into steam, and on the other handpreliminary compaction of the extrusion mass is carried out. Through apipe 206 leading into this zone 202, water for example can be fed toadjust the desired total moisture content of the mass. In the followingextruder zone 203--referred to here as the "shear zone"--the screw isshaped in such a way that it imparts a large amount of energy to themass while simultaneously greatly increasing the pressure andtemperature. The further processing zone 204 which follows after shearzone 203 is equipped with a pipe 207 through which, for example, ahydrophobic agent for the binder is supplied; in this zone the nowmelted mass is stabilized, binder-modifying agents are added or,however, in this zone the leads of the screw are increased or the numberof spirals on the screw is reduced in the case of a multi-spiral screw,with the result that partial, preliminary expansion and also "smoothing"of the extrusion mass takes place here A further pipe 208 leads into theejection zone 205 adjoining downstream in the material flow; materialssuch as a hot cross-linking plastic for applying an outer coating to theextruded boards can be added via this pipe to the mass while it is stillin its "melt-gel state" in order to modify its surface finish. Finally,the mass is extruded through the--in this case rectangular--heatableextruder nozzle 26 and, as a result of the ensuing decompression, theflat extrusion 4 immediately starts to expand spontaneously as part ofthe moisture which it contains turns to steam, and the extrusionincreases gradually in thickness while the density is reduced in zone 41after the product leaves the flat nozzle 26.

An extrusion cross-section limiting device 3 is provided to limit thethickness of the boards. The frame 31 in which this device is mounted isadvantageously equipped with oppositely arranged, preciselypositionable, upper and lower rollers 33 and 32 which can be movedtowards each other. The extruded product, which is expanding extremelyslowly due to the increase in viscosity brought about by the coolingprocess, is passed between these rollers and its cross sectional profileis exactly shaped and maintained so that finally an "endless board" ofthe desired thickness is obtained. The boards are then cut up intoportions of the desired size and any necessary finishing, for examplethe surface application of a hydrophobic agent, or similar, is carriedout.

When the surfaces of the preferably silicone-coated or teflon-coatedrollers 32 and 33 are appropriately formed, boards with any desiredsurface structure may be produced.

The broken lines in FIG. 1 also show how a coating foil 50 is passedover a deflection roller 52 of a foil-coating device 5, which is notshown here in any further detail, at the end of the expansion zone 41,then brought into contact with the upper surface of the extruded product4, and then deflected once more around the first of the upper rollers 33of the roller frame 3 of the dimension-control device. An "adhesivelayer" can be applied to the surface of the extrusion 4 by injecting anadhesive under pressure via the supply line 208 ahead of nozzle 26 intozone 205 of the extruder, e.g. via an annular duct arranged on theinside of the cylinder and opening towards the screws. This adhesivelayer serves to bond the foil 50 running through the roller frame 3firmly to the surface of the board 40, thereby forming a foil coating45.

A device similar to that shown for feeding foil 50 can, of course, alsobe provided for coating the underside of the extruded board.

The dimension-control device 30 shown in FIG. 2, which is used to limitthe cross sectional dimensions of the product, consists of rollers 311mounted in a frame 310 to guide upper and lower continuous belts 330 and320 which form an upper and lower "wall element" respectively runningcontinuously in the same direction of travel (see arrow) and at the samespeed as the extruded product 4. The belts 330 and 320 may be providedwith separate drives to move them at a speed matched to that of thespeed of the extrusion or, also, they may be designed as non-drivenbelts. A surface-coating medium can be supplied via a pipe 280 in theexit area 250 of the cylinder--not shown in detail here--of the extruder20, close to the flat nozzle 260. Because this coating medium is thenextruded together with the extrusion mass it forms an extremely integralbond with the extrusion 40.

The broken lines denote another surface-coating device 50 which isarranged transversely across zone 410 of the extrusion 40 just as itleaves the nozzle 260 and starts to undergo expansion. The lower surfaceof this device is provided with outlet openings for uniformlydistributing a surface-coating medium supplied via feed pipe 510. Asimilar type of system can, of course, be provided to apply a coatingmedium to the underside of the extrusion.

It goes without saying that, if the expanded lightweight board 40 isdesired to have a structured surface, the continuous belts 330 and 320may be designed with appropriate surface-texturing elements which shouldbe advantageously coated with a non-stick release agent, as mentionedabove.

Finally, the new use of shaped parts for the production of structuralelements, e.g. in furniture and structures, and for insulation and/orpackaging purposes, is also an important subject of the presentinvention. These parts are preferably made from fibre-based sectionsand/or boards in turn obtained from the components described above.Shaped parts produced from the method described above may be used in themanufacture of construction material, furniture material, structuralmaterial, insulating material, packaging material, or the like. Thepreferred shaped part possesses an essentially dense surface and isformed from at least one melted gel mixture which undergoes spontaneousexpansion immediately after being extruded and in which small particlesof a fibre-containing and/or fibre-shaped biogenic, high-molecularmaterial are distributed within an essentially structure-determiningmatrix containing a large number of small cavities. The matrix is basedon a melt of a binder formed with at least one biopolymeric naturalsubstance taken from at least one of the groups of starches, dextrins,pectins, collagens, proteins or caseins. The melt is hardened followingthe application of elevated temperature, elevated pressure and/ormechanical stress, and the percentage of the binder is 5-85 wt. %, andpreferably 10-50 wt. %, relative to the dry extrusion mass. Such shapedparts possess excellent mechanical strength, are resistant,"lightweight" and easy to manipulate, e.g. they can be cut and sandedwithout any problem, they may also exist in granulate form, and theyhave a pleasing outer appearance. They are long-lasting and have anunlimited range of applications extending from construction via interiordecor, automobile and other vehicular uses, all the way through toefficient lightweight packaging.

The use of shaped parts which are textured has the advantage that theparts are highly resistant to penetration by fluids, in particularwater, and they can therefore be used in areas of elevated relativehumidity, e.g. in the tropics, in cellars and basements, or also theyare suitable as packaging materials for fresh fruit or meat, especiallywhen they are additionally treated with a hydrophobic agent according toClaim 9. With their foam-like structure, the new shaped parts exhibitespecially high strength and a high degree of isotropy as regards theirmechanical properties and workability. Shaped parts having the densitiesmentioned in this Claim are preferred because of their "lightweight"characteristics while still retaining adequate mechanical stability.

The advantages which can be obtained by using shaped parts having areduced density and coated exceed the advantages already described. Inaddition to the enhanced surface finish provided by the coating layer, asandwich effect is also achieved which additionally improves thestability and distortion resistance of the product.

Using in particular board-shaped, expanded, shaped products inaccordance with the preferred embodiment offers the advantage that theycan be used without any problem in place of the hitherto customarilyused particle boards of the same thickness.

The invention will now be explained in more detail on the basis of thefollowing examples:

EXAMPLE 1

Manufacture of an expanded wood fibre board 60 wt. % wood chips between0 and 3 mm in size having a residual moisture content of 12%, 35 wt. %cassava meal having a residual moisture content of 12% and 5 wt. % tallresin, are fed as solids into a conical double-screw extruder whoseoperation is adjusted in such a way that the temperature in the mass is160° C. and the pressure in the mass is 150 bar close to the nozzle. Theplastic, gel-like molten mass is extruded through a heatable flat nozzleand converted into a continuous board product by carrying out suddendecompression and adjusting the expansion index to 3, and the product isthen transported to other areas of the plant for further processing.

The board product had a dense surface, a thickness of 20 mm, a densityof 0.48 t/m³, and a bending strength of 14.2 N/mm².

EXAMPLE 2

Crushed rice and natural rubber in proportions of 70 wt. % to 29 wt. %were fed continuously into a twin-screw extruder via separate fedmechanisms.

In the area of the sealing zone, water was continuously supplied to theextruder via a feed pipe in such quantities (approximately in the rangefrom 2 to 10 wt. % relative to 99% starting materials) that an extrusionmass having a uniform water content of 14 wt. % was transported into thecompression zone of the extruder. Through another feed pipe 1 wt %,relative to the solid starting components, of a 60% aqueous paraffinemulsion was fed into the "further processing zone" of the extruder.During stable, continuous operation the temperature in the mass was 165°C. and the pressure was 200 bar. Products of round cross section werecontinuously extruded through two circular openings each 1.5 cm indiameter while adjusting the expansion index to 6; then, while theextrusions were still slowly expanding, they were cut up into smallspherical granulates using a rotating knife. The pleasant-lookingpackaging filler obtained in this way was waterproof, and elastic butexhibited high shape-restoring forces and, lastly, possessed goodbiodegradability when disposed of as waste.

EXAMPLE 3

The same procedure as described in Example 2 was used, the onlydifference being that apart from crushed rice, up to 70 wt. % lessnatural rubber than in Example 2 namely 24 wt. %, and an additional 5wt. % of cellulose as a biogenic fibre material were added to theextruder and a packaging foil material approximately 1.5 mm thick wasextruded through a flat nozzle.

An elastics dimensionally stable, low-density non-woven product wasobtained which exhibited increasing shape-restoring properties and hightear strength in proportion to increasing application of pressure.

EXAMPLE 4

The following components and conditions were selected for the extrusionprocess:

    ______________________________________    Potato starch:       67.5 wt.%    Phthalic acid anhydride:                         2.5 wt.%    pH value             8 to 11                         (adjusted with                         30% strength NaOH)    Cellulose (from the paper industry)                         30%    Water contet of overall mixture                         16 wt. %    adjusted to    ______________________________________

Operating conditions:

    ______________________________________    Expansion index        4.5    Density                0.25 t/m.sup.3    Temperature of the mass                           150° C.    Pressure in the mass   120 bar    ______________________________________

Boards 3.5 mm thick were obtained and these are ideally suitable forpackaging fruit, producing thermal insulating containers for fresh snackfoods, etc., but they are still brittle enough to be broken up intosmaller pieces when disposed of as waste.

EXAMPLE

    ______________________________________    An extrusion mass having the composition    ______________________________________    Corn semolina  37 wt. %    Polyethylene   10 wt. %    Softwood chips 50 wt. % (particle size 1-10 mm)    Linseed oil    3 wt. %    ______________________________________

was extruded in a single-screw extruder to give a lightweight chipboard24 mm thick. The expansion index was 3.0 and the density of the boardobtained was 0.3 t/m³.

The operating conditions were as follows:

    ______________________________________    Temperature in the mass 145° C.    Pressure in the mass     90 bar    ______________________________________

The wood chipboard product obtained in this way was waterproof alsounder tropical conditions; it possessed a bending strength of 13.8 andwas a pleasant yellow-brown in colour.

Although the invention has been described with reference to thepreferred embodiment illustrated in the attached drawing figures, it isnoted that substitutions may be made and equivalents employed hereinwithout departing from the scope of the invention as recited in theclaims.

I claim:
 1. A process for manufacturing a shaped material comprising thesteps of:mixing a moist, natural fibrous material and a binder togetherto form a mixture, wherein the binder is selected from the groupconsisting of starches, dextrins, pectins, collagens, proteins, andcaseins, and wherein the fibrous material is selected from the groupconsisting of wood fibers, straw, husks, cardboard, and paper; adjustinga water content of the mixture to 6-25% by weight of the mixture to forman adjusted mixture; compacting and applying shear forces to theadjusted mixture in a screw extruder to increase pressure andtemperature until the binder melts to form a molten gel mixture; shapingthe molten gel mixture by passing the mixture through a shape-impartingnozzle attached to the extruder; and relieving pressure from the moltengel mixture immediately thereafter such that as moisture in the moltengel mixture turns to steam, spontaneous expansion of the molten gelmixture occurs and a structurally rigid fiber or chip-based shaped partselected from the group consisting of structural elements suitable forconstruction or interior decor, insulation elements, and packagingelements is formed which has a density lower than the overall density ofthe non-gaseous components of which it is made up but a relatively densesurface.
 2. A process according to claim 1, wherein the binder comprisesstarch and said starch comprises starch-containing plant parts selectedfrom the group consisting of cereals, grains, and starch-containingroots, tubers and stems, either comminuted or in a natural state.
 3. Aprocess according to claim 1, wherein the mixture further comprises aliquid expansion agent, which is miscible with water and selected fromthe group consisting of alcohols and ketones, which boil in a range from70 to 180° C. under atmospheric pressure.
 4. A process according toclaim 1, wherein the mixture further contains at least one bi- orpolyfunctional modifying agent capable of forming cross-linking bridgesbetween molecules of the binder, under conditions of extrusion, saidmodifying agent being selected from the group consisting ofshort-chained di- or polycarboxylic acids, di- or poly(thi)ols and theirderivatives, molecules containing tertiary amino acid groups, andpolyphosphoric acids.
 5. A process according to claim 1, wherein anexpansion index of the molten gel mixture after decompression is of avalue of 2-8.
 6. A process according to claim 1, further comprising astep of coating the molten gel mixture with a coating mass immediatelyafter the molten gel mixture is passed through the nozzle.
 7. A processaccording to claim 1, further comprising a step of limiting expansion ofthe shaped part to a predetermined cross-sectional dimension.
 8. Aprocess according to claim 7, further comprising a step of applying asurface coating to the shaped part as expansion of the part is beinglimited.
 9. A process according to claim 1, wherein a twin-screwextruder is used.
 10. A process according to claim 1, wherein a specificmechanical energy input ranging from 0.05-0.7 kWh per kg of the adjustedmixture is imparted to said mixture during the compacting step.
 11. Aprocess according to claim 10, wherein a specific mechanical energyinput ranging from 0.1-0.3 kWh per kg of said mixture is applied.
 12. Aprocess according to claim 1, wherein the pressure is increased to15-600 bar.
 13. A process according to claim 12, wherein the pressure isincreased to 20-250 bar.
 14. A process according to claim 1, wherein thetemperature of the molten gel mixture is increased to at least 100° C.15. A process according to claim 14, wherein the temperature of themolten gel mixture is increased to 125-250° C. during the compactingstep.
 16. A process according to claim 1, wherein the mixture contains10-50 wt. % binder.
 17. A process according to claim 1, wherein themolten gel mixture is subjected to a step of pre-expansion immediatelybefore said step of shaping.
 18. A process according to claim 1, whereinthe density of said shaped part is less than 1 t/m³.
 19. A processaccording to claim 1, wherein the shaped part is elastic and saidprocess further comprises mixing rubber or silicone with the fibrousmaterial and binder to form a shaped part having elasticcharacteristics.
 20. A process according to claim 1, wherein thestructurally rigid fiber or chip-based shaped part has a bendingstrength of at least 7 N/mm².
 21. A process according to claim 1,wherein the structurally rigid fiber or chip-based shaped part has abending strength of at least 14.5 N/mm².
 22. A process according toclaim 1, further comprising adding to said mixture before the shapingstep at least one hydrophobicity increasing agent selected from thegroup consisting of natural oils, synthetic oils, waxes, fats, resins,rubbers, paraffins, silicones, and plastics.
 23. A process formanufacturing a shaped material comprising the steps of:mixing a moist,natural fibrous material with 5 to 85 wt. % of a binder selected formthe group consisting of starches, dextrins, pectins, collagens,proteins, and caseins to form a mixture; adding to said mixture at leastone hydrophobicity increasing agent selected from the group consistingof natural oils, synthetic oils, waxes, fats, resins, rubbers,paraffins, silicones and plastics; adjusting a water content of themixture to 6-25% by weight of the mixture to form an adjusted mixture;compacting and applying shear forces to the adjusted mixture in a screwextruder to increase pressure and temperature until the binder melts toform a molten gel mixture; shaping the molten gel mixture by passing themixture through a shaped-imparting nozzle attached to the extruder; andrelieving pressure from the molten gel mixture immediately thereaftersuch that as moisture in the molten gel mixture turns to steam,spontaneous expansion of the molten gel mixture occurs and astructurally rigid, fiber or chip-based shaped part is formed which hasa density lower than the overall density of the non-gaseous componentsof which it is made up but a relatively dense surface.
 24. A processaccording to claim 23, wherein the binder comprises starch and saidstarch comprises starch-containing plant parts selected from the groupconsisting of cereals, grains, and starch-containing roots, tubers andstems, either comminuted or in a natural state.
 25. A process accordingto claim 23, wherein the fibrous material is selected from the groupconsisting of wood chips, plant fibers, cellulose materials, recycledcellulose materials, paper materials and recycled paper materials.
 26. Aprocess according to claim 23, wherein the mixture further comprises aliquid expansion agent, which is miscible with water and selected fromthe group consisting of alcohols and ketones which boil in a range from70 to 180° C. under atmospheric pressure.
 27. A process according toclaim 23, wherein the mixture further contains at least one bi- orpolyfunctional modifying agent capable of forming cross-linking bridgesbetween molecules of the binder, under conditions of extrusion, saidmodifying agent being selected from the group consisting ofshort-chained di- or polycarboxylic acids, di- or poly(thi)ols and theirderivatives, molecules containing tertiary amino acid groups, andpolyphosphoric acids.
 28. A process according to claim 23, wherein anexpansion index of the molten gel mixture after decompression is of avalue of 2-8.
 29. A process according to claim 23, further comprising astep of coating the molten gel mixture with a peripherally suppliedcoating mass before the molten gel mixture is passed through the nozzle.30. A process according to claim 23, further comprising a step oflimiting expansion of the shaped part to a predetermined cross-sectionaldimension.
 31. A process according to claim 30, further comprising astep of applying a surface coating to the shaped part as expansion ofthe part is being limited.
 32. A process according to claim 23, whereina twin-screw extruder is used.
 33. A process according to claim 23,wherein a specific mechanical energy input ranging from 0.05-0.7 kWh perkg of the adjusted mixture is imparted to said mixture during thecompacting step.
 34. A process according to claim 33, wherein a specificmechanical input ranging from 0.1-0.3 kWh per kg of said mixture isapplied.
 35. A process according to claim 23, wherein the pressure isincreased to 15-600 bar.
 36. A process according to claim 35, whereinthe pressure is increased to 20-250 bar.
 37. A process according toclaim 23, wherein the temperature of the molten gel mixture is increasedto at least 100° C.
 38. A process according to claim 37, wherein thetemperature of the molten gel mixture is increased to 125-250° C. duringthe compacting step.
 39. A process according to claim 23, wherein themixture contains 10-50 wt. % binder.
 40. A process according to claim23, wherein the molten gel mixture is subjected to a step ofpre-expansion immediately before said step of shaping.
 41. A processaccording to claim 23, wherein the density of said shaped part is lessthan 1 t/m³.
 42. A process according to claim 23, wherein the shapedpart is elastic and said process further comprises mixing rubber orsilicone with the fibrous material and binder to form a shaped parthaving elastic characteristics.
 43. A process according to claim 23,wherein the structurally rigid fiber or chip-based shaped part has abending strength of at least 7 N/mm².
 44. A process according to claim23, wherein the structurally rigid fiber or chip-based part has abending strength of at least 14.5 N/mm².
 45. A machine for implementinga process according to claim 1 or claim 23, wherein the machine isfitted with means for comminuting, conditioning, and pre-mixing thestarting components and also with means for feeding these components toan extruder having at least one shape-determining extrusion opening, theextruder including means for supplying solid, lump-shaped orsmall-particled starting components, and being provided upstream of thenozzle with a processing zone in which partial decompression of themixture being processed can be carried out, further comprising adimension limiting means positioned downstream of the extruder forlimiting expansion of the shaped part.
 46. A machine according to claim45, wherein the dimension limiting means includes at least onespeed-adjustable roller oriented essentially transverse to a directionof movement of the shaped part and having a non-adhesive surface, theroller being rotatable at a speed matched with a speed of passage of theshaped part.
 47. A machine according to claim 46, wherein a surface ofat least one roller is textured.
 48. A machine according to claim 45,wherein the dimension limiting means includes at least one endless beltthat is supported for movement along a run extending in a directionparallel to a direction of movement of the shaped part, the belt havinga non-adhesive surface and being movable at a speed matched with a speedof passage of the shaped part.
 49. A machine according to claim 48,wherein a surface of at least one endless belt is textured.
 50. Amachine according to claim 45, further comprising a coating means forplacing a coating foil against the shaped part upstream of the dimensionlimiting means.
 51. A machine for implementing the process according toclaim 1 or claim 23, wherein the machine is fitted with means forcomminuting, conditioning, and pre-mixing the starting components andalso with means for feeding these components to an extruder having atleast one shape-determining extrusion opening, the extruder includingmeans for supplying solid, lump-shaped or small-particled startingcomponents, and being provided upstream of the nozzle with a processingzone in which partial decompression of the mixture being processed canbe carried out, further comprising a plurality of feed pipes upstream ofan opening of the extruder, the feed pipes being arranged around acircumference of the extruder, said feed pipes supplying a coatingmaterial to the molten gel mixture.
 52. A process for manufacturing amaterial for use in structural elements, insulation and packagingcomprising the steps of:mixing a moist, natural, fibrous material and abinder together, wherein the binder is selected from the groupconsisting of starches, dextrins, pectins, collagens, proteins, andcaseins to form a mixture; adjusting a water content of the mixture to6-25% by weight of the mixture to form an adjusted mixture; compactingand applying shear forces to the adjusted mixture in a screw extruder toincrease pressure and temperature until the binder melts to form amolten gel mixture; shaping the molten gel mixture by passing themixture through a shape-imparting nozzle attached to the extruder;relieving pressure from the molten gel mixture immediately thereaftersuch that as moisture in the molten gel mixture turns to steam,spontaneous expansion of the molten gel mixture occurs and a fiber orchip-based shaped part is formed which has a density lower than theoverall density of the non-gaseous components of which it is made up buta relatively dense surface; and coating the molten gel mixture with aperipherally supplied coating mass before the molten gel mixture ispassed through the nozzle.